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Biochemistry MCQ

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Quiz on Biochemistry MCQ, created by #أطباء_2020 on 12/01/2015.
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Quiz by #أطباء_2020 , updated more than 1 year ago
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Created by #أطباء_2020 over 9 years ago
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Question 1

Question
what is the fate of lipid digestion products absorbed by intestinal mucosal cells?
Answer
  • export of short chain fatty acids to the portal blood
  • re-esteriification of long chain fatty acids forming triacylglycerols
  • formation of lipoprotein particles: chylomicron
  • all the above

Question 2

Question
after an overnight fast which of the following enzymes (proteins) show low activity?
Answer
  • glucokinase in liver
  • hexokinase in brain
  • GluT1 transporter
  • glucose 6 phosphatase in liver
  • α-ketoglutaric dehydrogenase in brain

Question 3

Question
which one of the following statements about prostaglandin synthesis is INCORRECT
Answer
  • Phospholipase A2 or phospholipase C release prostaglandin precursors from plasma membrane phospholipids
  • arachidonic acid is a major precursor of prostaglandins
  • Prostaglandins are derived from an essential fatty acid
  • prostaglandins are produced through the action of lipoxygenase
  • prostaglandins synthesis is inhibited by glucocorticoids and aspirin

Question 4

Question
uncoupling of oxidative phosphorylation could occur with
Answer
  • A high concentration of glucocorticoids
  • A high concentration of thyroxine
  • A high concentration of adrenaline
  • A high concentration of insulin
  • A high concentration of glucagon

Question 5

Question
sodium-glucose transporter in the intestine
Answer
  • act as symport
  • is located at the serosal side of the intestinal cell membrane
  • binds ATP
  • transport both sodium and glucose concentration gradient

Question 6

Question
GLUT 2 in liver cells and pancreatic β cells
Answer
  • has low Km (high affinity to glucose)
  • is suitable for glucose uptake during fasting
  • acts as glucose sensor , along with glucokinase , in β-cells of pancreas
  • all the above

Question 7

Question
according to Pasteur effect
Answer
  • glycolysis proceeds in a faster rate in presence of oxygen
  • oxygen decreases the rate of glycolysis
  • glycolysis produces more ATP from a glucose molecule in absence of oxygen
  • oxygen decreases the production of ATP from one glucose molecule

Question 8

Question
the bi-functional enzyme PFK2/fructose2,6-bisphosphatase
Answer
  • controls the level of fructose 2,6-bisphosphate ,hence the activity of PFK1
  • is phosphorylated by cAMP-dependant protein kinase under the effect of glucagon and epinephrine
  • is dephosphorylated by protein phosphatase under the effect of insulin
  • all the above

Question 9

Question
which of the following is true about fatty acid oxidation
Answer
  • the active form of fatty acid is fatty acyl coA
  • fatty acid is activated by acyl coA synthetase of the inner mitochondrial membrane
  • with fatty acid activation ATP is hydrolyzed to ADP + inorganic phosphate
  • Fatty acyl coA is used only for energy production

Question 10

Question
deficiency of carnitine acyl transferase may NOT lead to
Answer
  • failure of fatty acid oxidation
  • hypoglycemia
  • ketoacidosis
  • hepatomegaly , seizures and cardiomyopathy leading to infantile death

Question 11

Question
mitochondrial β-oxidation pathway produces propionyl CoA from
Answer
  • fatty acid with odd number of carbons
  • phytanic acid derived from chlorophyll
  • both (A) & (b)
  • neither (A) nor (B)

Question 12

Question
Zellweger's (cerebro-hepato-renal) syndrome is characterizd by accumulation
Answer
  • phytanic acid
  • very long chain polyenoic acid
  • both (A) & (B)
  • neither (A) nor (B)

Question 13

Question
ِAn enzyme is not involved in glycolysis in muscle is
Answer
  • aldolase
  • glyceraldehyde 3-phosphate dehydrogenase
  • enolase
  • pyruvate kinase
  • bisphosphoglycerate mutase

Question 14

Question
the best description of the difference between glucokinase and hexokinase is
Answer
  • hexokinase is found in liver and kidney , while hexokinase is present in nearly all tissues
  • hexokinase has much higher Km for glucose
  • glucokinase is found only in tissues that are totally dependent on glucose for fuel , such as brain & RBCs
  • glucokinase & hexokinase are zymogens
  • glucokinase but not hexokinase is induced by insulin

Question 15

Question
An abnormal accumulation of galactose 1-p in liver is usually caused by a deficiency
Answer
  • glucose 6-phosphate dehydrogenase
  • glucose 6-phosphatse
  • galactokinase
  • galactose 1-phosphate uridylyl transferase
  • hexokinase

Question 16

Question
the oxidative decarboxylation of all α-keto acids is similar to that of pyruvate. A common requirment for all is
Answer
  • NADP
  • Acetyl CoA
  • Lipoic acid
  • α -ketoglutarate
  • GDP

Question 17

Question
mitochondria in brown fat of human infants increase heat generation .this result from an increased rate of electron transport due to
Answer
  • inhibition of ADP-ATP antiporter
  • inhibition of F1-Fo ATP synthase
  • blockage of NADH reoxidation
  • increased permeability of the inner mitochondrial membrane
  • decreased rate of oxygen consumption

Question 18

Question
all the electron carrying groups of the respiratory chain
Answer
  • are fixed to the inner mitochondrial membrane
  • are arranged in an order of descending redox potential
  • contain iron as an electron acceptor
  • participate in the building up of the proton gradient
  • none of the above

Question 19

Question
the following enzyme is a constituent of pentose phosphate pathway
Answer
  • glucose 6-phosphatase
  • phosphorylase
  • hexokinase
  • glucose 6-phosphate dehydrogenase
  • phosphohexoisomerase

Question 20

Question
a substance that is not an intermediate in formation of glucuronic acid from glucose
Answer
  • UDP-galactose
  • UDP-glucose
  • Glucose 6-phosphate
  • UDP-glucuronic acid
  • glucose 1-phosphate

Question 21

Question
in the break down of muscle glycogen the predominant product is
Answer
  • glucose
  • glucose 1-phosphate
  • UDP-glucose
  • maltose
  • maltriose

Question 22

Question
the regulation of glycogenolysis in muscle differ from that in the liver
Answer
  • muscles lack receptors of glucagon
  • only the liver uses β-adrenergic receptors for this regulation
  • only muscles respond to epinephrine
  • muscle glycogenolysis does not respond to stimulation by intracellular calcium
  • muscle produces mostly glucose from glycogen

Question 23

Question
mammalian fatty acids desaturase systems introduce double bonds
Answer
  • at Δ4, Δ5, Δ6, Δ9 positions
  • at ω3, ω6 and ω9 positions
  • between an existing double bond and methyl carbon
  • all the above

Question 24

Question
lypolysis in adipose tissue is initiated by
Answer
  • Food intake
  • ketoacidosis
  • fasting
  • high insulin/glucagon ratio
  • high fatty acid concentration

Question 25

Question
The enzyme required for both the synthesis of acetoacetate and its utilization as a fuel is
Answer
  • succinyl coA : acetoacetate CoA transferase
  • HMG-CoA synthase
  • thiolase
  • HMG-CoA lyase
  • β-hydroxybutyrate dehydrogenase

Question 26

Question
Receptor-mediated uptake of excess LDL results in all the following Except
Answer
  • increased estrification of cholesterol
  • increased production of mevalonate
  • decreased synthesis of HMG-CoA reductase
  • decreased synthesis of the LDL recepttor
  • decreased receptor-mediated endocytosis of LDL

Question 27

Question
In man serum lipoprotein fraction with the highest cholesterol content is
Answer
  • α-lipoprotein
  • β-lipoprotein
  • pre β-lipoprotein
  • chylomicrons
  • pre-albumin

Question 28

Question
secondary bile acids are distinguishable from the primary bile acids because they lack
Answer
  • glycine
  • taurine
  • a hydroxyl group
  • a methyl group
  • a carboxylate group

Question 29

Question
what is the enzyme used for cholesterol storage
Answer
  • HMG-CoA reductase
  • Lecithin cholesterol acyl transferase
  • lipoprotein lipase
  • Acyl CoA cholesterol acyl transferase
  • cholesterol esterase

Question 30

Question
cori cycle transfers
Answer
  • alanine from muscle to liver
  • lactic from liver to muscle
  • lactic from exercising muscle or RBCs to liver
  • Glucose from muscle to liver
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